I gave 8.5 a go. Didn't like it very much, Campaign seemed pretty much like vanilla, didn't notice much difference, but battle mechanics made battle too easy.
I played Prussian, H/H with ultra units.
1. First battle against several Citizenry units. By numbers sides were equal, AI was bit stronger but I had line infantry and two cav units. In the battle my side received 38 casualties but AI lost 700-800. During the battle one of my cav units charged on one citizenry unit. Result: my cavallery had no casualties at all, enemy citizenry routed after few seconds when they lost about 30 guys. Then my cavalry hunted the rest 130 citizens. Cavalry is overpowered in vanilla, but still.
At one point a citizen unit went inside the town hall. I decided to let my guys shoot at them for a while before entering. I moved three units close. After few of minutes of intensive shooting my units had lost 40 guys in total. They lost a single man. And I believe it was because of friendly fire. Now, I don't feel it's very realistic. If someone shoots at you, you can shoot at him. If you are in the open, and he hides most of the time, sure he has better chance to kill you, but he still has to come to the window to shoot. Then is your chance, as you know he will be in that window. This is how it is done even in those days. In these cases people in buildings died too. Vanilla is much closer to reality in this way.
2. After the battle I moved my army and left only two weak units to defend the city. Bavarians declared a war and marched their army (bigger one) over the border. I moved my army back to meet theirs and then noticed that I made a mistake. Enemy could easily go round and take the city without a threat. On their turn Bavarians moved beside to the city, and then walked back. Well lucky me!
3. I attacked Bavarians. Both armies almost equal, except I had one artillery more but one line infantry less. My side suffered less than 200 losses, theirs over 700. Some of it because of constant friendly fire, their second line tried to fire through their first line.
4. In the east Courland started a war. Polish minded their own business, though in my earlier Prussian game they harassed me all the time. Courlanders moved an army on my land and I attacked it. Equal on size, but their infantry was all militia as mine was infantry. I still suspected the battle to be costly. Well. Forget it. My side lost 200, theirs 1500. My side lost that much, as I forgot to turn off artillery when I moved my infantry forwards. Their militia routed all the time. My cavalry units got many stripes for their "heroic" deeds.
This was enough. I don't want to put anyone down, as I've made mods and helped to make them in different games and I respect the hard work without pay modders do. But this is honest feedback from one person. I sincerely feel vanilla AI acted better and it's mechanics are tuned better. And yes, more realistic.